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 $81.39   12.374%   $91.4612   $91.46   $91.45   $91.50  
  Purchase #2 $33.92   7.190%   $36.3588   $36.36   $36.35   $36.40  
  Purchase #3 $125.94   12.787%   $142.0439   $142.04   $142.05   $142.00  
  Purchase #4 $176.67   7.560%   $190.0263   $190.03   $190.05   $190.00  
  Purchase #5 $187.83   9.654%   $205.9631   $205.96   $205.95   $206.00  
  Purchase #6 $59.74   3.833%   $62.0298   $62.03   $62.05   $62.00  
  Purchase #7 $147.42   12.470%   $165.8033   $165.80   $165.80   $165.80  
  7 purchase totals = $812.91       $893.6864   $893.68   $893.70   $893.70