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 $232.48   9.408%   $254.3517   $254.35   $254.35   $254.40  
  Purchase #2 $245.59   7.533%   $264.0903   $264.09   $264.10   $264.10  
  Purchase #3 $224.66   7.559%   $241.642   $241.64   $241.65   $241.60  
  Purchase #4 $32.52   5.225%   $34.2192   $34.22   $34.20   $34.20  
  Purchase #5 $97.63   3.352%   $100.9026   $100.90   $100.90   $100.90  
  Purchase #6 $234.65   6.784%   $250.5687   $250.57   $250.55   $250.60  
  Purchase #7 $6.36   10.273%   $7.0134   $7.01   $7.00   $7.00  
  7 purchase totals = $1,073.89       $1,152.7879   $1,152.78   $1,152.75   $1,152.80