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 $149.47   4.491%   $156.1827   $156.18   $156.20   $156.20  
  Purchase #2 $62.90   11.267%   $69.9869   $69.99   $70.00   $70.00  
  Purchase #3 $149.26   10.227%   $164.5248   $164.52   $164.50   $164.50  
  Purchase #4 $56.78   7.714%   $61.16   $61.16   $61.15   $61.20  
  Purchase #5 $134.62   11.618%   $150.2602   $150.26   $150.25   $150.30  
  Purchase #6 $160.41   7.344%   $172.1905   $172.19   $172.20   $172.20  
  Purchase #7 $168.84   12.740%   $190.3502   $190.35   $190.35   $190.40  
  7 purchase totals = $882.28       $964.6553   $964.65   $964.65   $964.80