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 $238.41   10.469%   $263.3691   $263.37   $263.35   $263.40  
  Purchase #2 $127.34   6.192%   $135.2249   $135.22   $135.20   $135.20  
  Purchase #3 $204.44   6.861%   $218.4666   $218.47   $218.45   $218.50  
  Purchase #4 $243.79   9.638%   $267.2865   $267.29   $267.30   $267.30  
  Purchase #5 $54.77   8.559%   $59.4578   $59.46   $59.45   $59.50  
  Purchase #6 $182.96   10.144%   $201.5195   $201.52   $201.50   $201.50  
  Purchase #7 $41.81   11.205%   $46.4948   $46.49   $46.50   $46.50  
  7 purchase totals = $1,093.52       $1,191.8192   $1,191.82   $1,191.75   $1,191.90