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 $142.94   11.478%   $159.3467   $159.35   $159.35   $159.30  
  Purchase #2 $205.88   7.489%   $221.2984   $221.30   $221.30   $221.30  
  Purchase #3 $196.39   7.263%   $210.6538   $210.65   $210.65   $210.70  
  Purchase #4 $57.77   7.453%   $62.0756   $62.08   $62.10   $62.10  
  Purchase #5 $156.98   11.126%   $174.4456   $174.45   $174.45   $174.40  
  Purchase #6 $209.79   3.822%   $217.8082   $217.81   $217.80   $217.80  
  Purchase #7 $13.45   4.456%   $14.0493   $14.05   $14.05   $14.00  
  7 purchase totals = $983.20       $1,059.6776   $1,059.69   $1,059.70   $1,059.60