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 $36.34   3.363%   $37.5621   $37.56   $37.55   $37.60  
  Purchase #2 $236.43   9.441%   $258.7514   $258.75   $258.75   $258.80  
  Purchase #3 $230.80   4.775%   $241.8207   $241.82   $241.80   $241.80  
  Purchase #4 $224.67   13.656%   $255.3509   $255.35   $255.35   $255.40  
  Purchase #5 $49.70   8.702%   $54.0249   $54.02   $54.00   $54.00  
  Purchase #6 $89.41   9.205%   $97.6402   $97.64   $97.65   $97.60  
  Purchase #7 $59.48   6.127%   $63.1243   $63.12   $63.10   $63.10  
  7 purchase totals = $926.83       $1,008.2745   $1,008.26   $1,008.20   $1,008.30