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 $189.32   6.341%   $201.3248   $201.32   $201.30   $201.30  
  Purchase #2 $218.41   11.663%   $243.8832   $243.88   $243.90   $243.90  
  Purchase #3 $209.99   5.615%   $221.7809   $221.78   $221.80   $221.80  
  Purchase #4 $36.96   12.788%   $41.6864   $41.69   $41.70   $41.70  
  Purchase #5 $61.26   5.565%   $64.6691   $64.67   $64.65   $64.70  
  Purchase #6 $85.87   6.193%   $91.1879   $91.19   $91.20   $91.20  
  Purchase #7 $149.68   12.543%   $168.4544   $168.45   $168.45   $168.50  
  7 purchase totals = $951.49       $1,032.9867   $1,032.98   $1,033.00   $1,033.10