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 $87.49   5.827%   $92.588   $92.59   $92.60   $92.60  
  Purchase #2 $231.84   9.425%   $253.6909   $253.69   $253.70   $253.70  
  Purchase #3 $210.89   5.532%   $222.5564   $222.56   $222.55   $222.60  
  Purchase #4 $235.56   3.235%   $243.1804   $243.18   $243.20   $243.20  
  Purchase #5 $122.56   7.146%   $131.3181   $131.32   $131.30   $131.30  
  Purchase #6 $232.33   5.476%   $245.0524   $245.05   $245.05   $245.10  
  Purchase #7 $181.38   4.791%   $190.0699   $190.07   $190.05   $190.10  
  7 purchase totals = $1,302.05       $1,378.4561   $1,378.46   $1,378.45   $1,378.60