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 $179.26   5.783%   $189.6266   $189.63   $189.65   $189.60  
  Purchase #2 $165.53   5.595%   $174.7914   $174.79   $174.80   $174.80  
  Purchase #3 $194.94   12.317%   $218.9508   $218.95   $218.95   $219.00  
  Purchase #4 $24.62   10.829%   $27.2861   $27.29   $27.30   $27.30  
  Purchase #5 $84.66   5.334%   $89.1758   $89.18   $89.20   $89.20  
  Purchase #6 $220.25   12.650%   $248.1116   $248.11   $248.10   $248.10  
  Purchase #7 $188.57   7.630%   $202.9579   $202.96   $202.95   $203.00  
  7 purchase totals = $1,057.83       $1,150.9002   $1,150.91   $1,150.95   $1,151.00