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 $213.27   11.118%   $236.9814   $236.98   $237.00   $237.00  
  Purchase #2 $156.40   11.774%   $174.8145   $174.81   $174.80   $174.80  
  Purchase #3 $129.65   6.542%   $138.1317   $138.13   $138.15   $138.10  
  Purchase #4 $33.81   7.792%   $36.4445   $36.44   $36.45   $36.40  
  Purchase #5 $177.79   5.349%   $187.3   $187.30   $187.30   $187.30  
  Purchase #6 $67.46   11.159%   $74.9879   $74.99   $75.00   $75.00  
  Purchase #7 $187.44   9.676%   $205.5767   $205.58   $205.60   $205.60  
  7 purchase totals = $965.82       $1,054.2367   $1,054.23   $1,054.30   $1,054.20