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 $195.48   8.432%   $211.9629   $211.96   $211.95   $212.00  
  Purchase #2 $243.45   10.319%   $268.5716   $268.57   $268.55   $268.60  
  Purchase #3 $16.65   11.621%   $18.5849   $18.58   $18.60   $18.60  
  Purchase #4 $239.59   8.760%   $260.5781   $260.58   $260.60   $260.60  
  Purchase #5 $94.43   7.813%   $101.8078   $101.81   $101.80   $101.80  
  Purchase #6 $55.36   9.857%   $60.8168   $60.82   $60.80   $60.80  
  Purchase #7 $74.34   7.642%   $80.0211   $80.02   $80.00   $80.00  
  7 purchase totals = $919.30       $1,002.3432   $1,002.34   $1,002.30   $1,002.40