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 $223.79   5.242%   $235.5211   $235.52   $235.50   $235.50  
  Purchase #2 $215.27   10.815%   $238.5515   $238.55   $238.55   $238.60  
  Purchase #3 $84.67   9.275%   $92.5231   $92.52   $92.50   $92.50  
  Purchase #4 $204.93   11.601%   $228.7039   $228.70   $228.70   $228.70  
  Purchase #5 $187.74   8.833%   $204.3231   $204.32   $204.30   $204.30  
  Purchase #6 $54.91   13.823%   $62.5002   $62.50   $62.50   $62.50  
  Purchase #7 $160.44   11.693%   $179.2002   $179.20   $179.20   $179.20  
  7 purchase totals = $1,131.75       $1,241.3231   $1,241.31   $1,241.25   $1,241.30