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 $32.61   11.444%   $36.3419   $36.34   $36.35   $36.30  
  Purchase #2 $244.45   10.353%   $269.7579   $269.76   $269.75   $269.80  
  Purchase #3 $105.55   13.487%   $119.7855   $119.79   $119.80   $119.80  
  Purchase #4 $48.38   4.286%   $50.4536   $50.45   $50.45   $50.50  
  Purchase #5 $223.52   9.154%   $243.981   $243.98   $244.00   $244.00  
  Purchase #6 $86.45   9.167%   $94.3749   $94.37   $94.35   $94.40  
  Purchase #7 $189.77   13.869%   $216.0892   $216.09   $216.10   $216.10  
  7 purchase totals = $930.73       $1,030.7840   $1,030.78   $1,030.80   $1,030.90