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 $68.40   9.281%   $74.7482   $74.75   $74.75   $74.70  
  Purchase #2 $171.34   10.515%   $189.3564   $189.36   $189.35   $189.40  
  Purchase #3 $246.28   12.767%   $277.7226   $277.72   $277.70   $277.70  
  Purchase #4 $58.93   10.262%   $64.9774   $64.98   $65.00   $65.00  
  Purchase #5 $67.45   9.451%   $73.8247   $73.82   $73.80   $73.80  
  Purchase #6 $201.58   12.279%   $226.332   $226.33   $226.35   $226.30  
  Purchase #7 $219.76   13.766%   $250.0122   $250.01   $250.00   $250.00  
  7 purchase totals = $1,033.74       $1,156.9735   $1,156.97   $1,156.95   $1,156.90