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 $190.41   8.232%   $206.0846   $206.08   $206.10   $206.10  
  Purchase #2 $152.97   7.289%   $164.12   $164.12   $164.10   $164.10  
  Purchase #3 $83.65   5.203%   $88.0023   $88.00   $88.00   $88.00  
  Purchase #4 $98.87   12.148%   $110.8807   $110.88   $110.90   $110.90  
  Purchase #5 $246.69   11.636%   $275.3948   $275.39   $275.40   $275.40  
  Purchase #6 $79.46   9.822%   $87.2646   $87.26   $87.25   $87.30  
  Purchase #7 $74.70   5.607%   $78.8884   $78.89   $78.90   $78.90  
  7 purchase totals = $926.75       $1,010.6354   $1,010.62   $1,010.65   $1,010.70