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 $94.82   10.283%   $104.5703   $104.57   $104.55   $104.60  
  Purchase #2 $177.59   8.523%   $192.726   $192.73   $192.75   $192.70  
  Purchase #3 $94.35   12.846%   $106.4702   $106.47   $106.45   $106.50  
  Purchase #4 $191.71   9.874%   $210.6394   $210.64   $210.65   $210.60  
  Purchase #5 $90.51   6.791%   $96.6565   $96.66   $96.65   $96.70  
  Purchase #6 $161.95   5.347%   $170.6095   $170.61   $170.60   $170.60  
  Purchase #7 $207.86   5.754%   $219.8203   $219.82   $219.80   $219.80  
  7 purchase totals = $1,018.79       $1,101.4922   $1,101.50   $1,101.45   $1,101.50