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 $49.29   4.334%   $51.4262   $51.43   $51.45   $51.40  
  Purchase #2 $213.56   6.129%   $226.6491   $226.65   $226.65   $226.60  
  Purchase #3 $95.32   10.807%   $105.6212   $105.62   $105.60   $105.60  
  Purchase #4 $198.68   6.734%   $212.0591   $212.06   $212.05   $212.10  
  Purchase #5 $141.41   6.554%   $150.678   $150.68   $150.70   $150.70  
  Purchase #6 $153.95   8.347%   $166.8002   $166.80   $166.80   $166.80  
  Purchase #7 $217.90   11.501%   $242.9607   $242.96   $242.95   $243.00  
  7 purchase totals = $1,070.11       $1,156.1945   $1,156.20   $1,156.20   $1,156.20