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 $155.89   11.586%   $173.9514   $173.95   $173.95   $174.00  
  Purchase #2 $52.33   8.621%   $56.8414   $56.84   $56.85   $56.80  
  Purchase #3 $163.87   3.302%   $169.281   $169.28   $169.30   $169.30  
  Purchase #4 $173.36   12.661%   $195.3091   $195.31   $195.30   $195.30  
  Purchase #5 $166.55   3.482%   $172.3493   $172.35   $172.35   $172.30  
  Purchase #6 $223.92   7.285%   $240.2326   $240.23   $240.25   $240.20  
  Purchase #7 $38.26   3.394%   $39.5585   $39.56   $39.55   $39.60  
  7 purchase totals = $974.18       $1,047.5233   $1,047.52   $1,047.55   $1,047.50