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 $147.89   6.168%   $157.0119   $157.01   $157.00   $157.00  
  Purchase #2 $107.83   13.296%   $122.1671   $122.17   $122.15   $122.20  
  Purchase #3 $91.70   4.173%   $95.5266   $95.53   $95.55   $95.50  
  Purchase #4 $48.52   11.821%   $54.2555   $54.26   $54.25   $54.30  
  Purchase #5 $227.67   12.395%   $255.8897   $255.89   $255.90   $255.90  
  Purchase #6 $25.58   3.436%   $26.4589   $26.46   $26.45   $26.50  
  Purchase #7 $226.39   11.224%   $251.8   $251.80   $251.80   $251.80  
  7 purchase totals = $875.58       $963.1097   $963.12   $963.10   $963.20