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 $93.74   3.822%   $97.3227   $97.32   $97.30   $97.30  
  Purchase #2 $203.39   8.766%   $221.2192   $221.22   $221.20   $221.20  
  Purchase #3 $97.79   8.642%   $106.241   $106.24   $106.25   $106.20  
  Purchase #4 $215.31   5.107%   $226.3059   $226.31   $226.30   $226.30  
  Purchase #5 $217.31   11.305%   $241.8769   $241.88   $241.90   $241.90  
  Purchase #6 $82.50   3.790%   $85.6268   $85.63   $85.65   $85.60  
  Purchase #7 $80.75   11.603%   $90.1194   $90.12   $90.10   $90.10  
  7 purchase totals = $990.79       $1,068.7119   $1,068.72   $1,068.70   $1,068.60