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 $53.52   10.511%   $59.1455   $59.15   $59.15   $59.10  
  Purchase #2 $175.67   12.726%   $198.0258   $198.03   $198.05   $198.00  
  Purchase #3 $211.67   5.765%   $223.8728   $223.87   $223.85   $223.90  
  Purchase #4 $52.39   7.139%   $56.1301   $56.13   $56.15   $56.10  
  Purchase #5 $8.75   11.445%   $9.7514   $9.75   $9.75   $9.80  
  Purchase #6 $14.77   11.204%   $16.4248   $16.42   $16.40   $16.40  
  Purchase #7 $172.94   10.489%   $191.0797   $191.08   $191.10   $191.10  
  7 purchase totals = $689.71       $754.4301   $754.43   $754.45   $754.40