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 $108.67   11.358%   $121.0127   $121.01   $121.00   $121.00  
  Purchase #2 $61.75   10.681%   $68.3455   $68.35   $68.35   $68.30  
  Purchase #3 $54.46   5.676%   $57.5511   $57.55   $57.55   $57.60  
  Purchase #4 $245.75   11.266%   $273.4362   $273.44   $273.45   $273.40  
  Purchase #5 $210.46   7.276%   $225.7731   $225.77   $225.75   $225.80  
  Purchase #6 $185.53   10.317%   $204.6711   $204.67   $204.65   $204.70  
  Purchase #7 $102.49   6.398%   $109.0473   $109.05   $109.05   $109.00  
  7 purchase totals = $969.11       $1,059.8370   $1,059.84   $1,059.80   $1,059.80