Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.86   8.519%   $106.1967   $106.20   $106.20   $106.20  
  Purchase #2 $166.47   11.116%   $184.9748   $184.97   $184.95   $185.00  
  Purchase #3 $132.64   11.790%   $148.2783   $148.28   $148.30   $148.30  
  Purchase #4 $185.62   9.507%   $203.2669   $203.27   $203.25   $203.30  
  Purchase #5 $104.32   9.782%   $114.5246   $114.52   $114.50   $114.50  
  Purchase #6 $131.55   5.118%   $138.2827   $138.28   $138.30   $138.30  
  Purchase #7 $143.32   9.752%   $157.2966   $157.30   $157.30   $157.30  
  7 purchase totals = $961.78       $1,052.8206   $1,052.82   $1,052.80   $1,052.90