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 $121.51   10.290%   $134.0134   $134.01   $134.00   $134.00  
  Purchase #2 $207.83   5.148%   $218.5291   $218.53   $218.55   $218.50  
  Purchase #3 $39.39   10.319%   $43.4547   $43.45   $43.45   $43.50  
  Purchase #4 $61.88   7.190%   $66.3292   $66.33   $66.35   $66.30  
  Purchase #5 $206.86   13.848%   $235.506   $235.51   $235.50   $235.50  
  Purchase #6 $143.68   12.141%   $161.1242   $161.12   $161.10   $161.10  
  Purchase #7 $200.84   4.641%   $210.161   $210.16   $210.15   $210.20  
  7 purchase totals = $981.99       $1,069.1176   $1,069.11   $1,069.10   $1,069.10