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 $188.75   3.194%   $194.7787   $194.78   $194.80   $194.80  
  Purchase #2 $68.51   9.385%   $74.9397   $74.94   $74.95   $74.90  
  Purchase #3 $157.64   7.644%   $169.69   $169.69   $169.70   $169.70  
  Purchase #4 $166.74   6.765%   $178.02   $178.02   $178.00   $178.00  
  Purchase #5 $71.82   10.717%   $79.5169   $79.52   $79.50   $79.50  
  Purchase #6 $205.26   7.617%   $220.8947   $220.89   $220.90   $220.90  
  Purchase #7 $201.96   11.512%   $225.2096   $225.21   $225.20   $225.20  
  7 purchase totals = $1,060.68       $1,143.0496   $1,143.05   $1,143.05   $1,143.00