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 $172.69   3.760%   $179.1831   $179.18   $179.20   $179.20  
  Purchase #2 $188.97   3.539%   $195.6576   $195.66   $195.65   $195.70  
  Purchase #3 $69.36   6.707%   $74.012   $74.01   $74.00   $74.00  
  Purchase #4 $144.29   3.575%   $149.4484   $149.45   $149.45   $149.40  
  Purchase #5 $23.52   13.343%   $26.6583   $26.66   $26.65   $26.70  
  Purchase #6 $179.78   5.576%   $189.8045   $189.80   $189.80   $189.80  
  Purchase #7 $133.99   3.602%   $138.8163   $138.82   $138.80   $138.80  
  7 purchase totals = $912.60       $953.5802   $953.58   $953.55   $953.60