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 $69.71   5.836%   $73.7783   $73.78   $73.80   $73.80  
  Purchase #2 $224.43   10.217%   $247.36   $247.36   $247.35   $247.40  
  Purchase #3 $71.70   9.488%   $78.5029   $78.50   $78.50   $78.50  
  Purchase #4 $69.62   8.755%   $75.7152   $75.72   $75.70   $75.70  
  Purchase #5 $105.69   9.751%   $115.9958   $116.00   $116.00   $116.00  
  Purchase #6 $128.96   7.229%   $138.2825   $138.28   $138.30   $138.30  
  Purchase #7 $157.29   6.386%   $167.3345   $167.33   $167.35   $167.30  
  7 purchase totals = $827.40       $896.9692   $896.97   $897.00   $897.00