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 $88.84   6.350%   $94.4813   $94.48   $94.50   $94.50  
  Purchase #2 $195.53   11.673%   $218.3542   $218.35   $218.35   $218.40  
  Purchase #3 $40.91   12.429%   $45.9947   $45.99   $46.00   $46.00  
  Purchase #4 $196.65   3.330%   $203.1984   $203.20   $203.20   $203.20  
  Purchase #5 $145.36   6.457%   $154.7459   $154.75   $154.75   $154.70  
  Purchase #6 $202.93   12.196%   $227.6793   $227.68   $227.70   $227.70  
  Purchase #7 $52.55   7.120%   $56.2916   $56.29   $56.30   $56.30  
  7 purchase totals = $922.77       $1,000.7454   $1,000.74   $1,000.80   $1,000.80