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 $108.35   10.159%   $119.3573   $119.36   $119.35   $119.40  
  Purchase #2 $10.60   11.814%   $11.8523   $11.85   $11.85   $11.90  
  Purchase #3 $242.58   9.634%   $265.9502   $265.95   $265.95   $266.00  
  Purchase #4 $220.85   5.277%   $232.5043   $232.50   $232.50   $232.50  
  Purchase #5 $23.29   9.732%   $25.5566   $25.56   $25.55   $25.60  
  Purchase #6 $103.34   10.378%   $114.0646   $114.06   $114.05   $114.10  
  Purchase #7 $202.97   11.113%   $225.5261   $225.53   $225.55   $225.50  
  7 purchase totals = $911.98       $994.8114   $994.81   $994.80   $995.00