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 $92.86   3.148%   $95.7832   $95.78   $95.80   $95.80  
  Purchase #2 $110.89   10.447%   $122.4747   $122.47   $122.45   $122.50  
  Purchase #3 $122.70   4.185%   $127.835   $127.84   $127.85   $127.80  
  Purchase #4 $201.73   7.628%   $217.118   $217.12   $217.10   $217.10  
  Purchase #5 $172.55   12.755%   $194.5588   $194.56   $194.55   $194.60  
  Purchase #6 $39.36   13.481%   $44.6661   $44.67   $44.65   $44.70  
  Purchase #7 $206.40   4.787%   $216.2804   $216.28   $216.30   $216.30  
  7 purchase totals = $946.49       $1,018.7162   $1,018.72   $1,018.70   $1,018.80