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 $237.27   11.661%   $264.9381   $264.94   $264.95   $264.90  
  Purchase #2 $89.30   5.630%   $94.3276   $94.33   $94.35   $94.30  
  Purchase #3 $56.99   5.487%   $60.117   $60.12   $60.10   $60.10  
  Purchase #4 $14.51   9.102%   $15.8307   $15.83   $15.85   $15.80  
  Purchase #5 $7.37   7.591%   $7.9295   $7.93   $7.95   $7.90  
  Purchase #6 $235.61   3.563%   $244.0048   $244.00   $244.00   $244.00  
  Purchase #7 $45.31   6.663%   $48.329   $48.33   $48.35   $48.30  
  7 purchase totals = $686.36       $735.4767   $735.48   $735.55   $735.30