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 $184.49   10.453%   $203.7747   $203.77   $203.75   $203.80  
  Purchase #2 $54.57   10.721%   $60.4204   $60.42   $60.40   $60.40  
  Purchase #3 $65.98   12.323%   $74.1107   $74.11   $74.10   $74.10  
  Purchase #4 $55.51   11.708%   $62.0091   $62.01   $62.00   $62.00  
  Purchase #5 $183.33   10.290%   $202.1947   $202.19   $202.20   $202.20  
  Purchase #6 $99.49   5.237%   $104.7003   $104.70   $104.70   $104.70  
  Purchase #7 $63.80   10.461%   $70.4741   $70.47   $70.45   $70.50  
  7 purchase totals = $707.17       $777.6840   $777.67   $777.60   $777.70