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 $118.79   12.467%   $133.5995   $133.60   $133.60   $133.60  
  Purchase #2 $103.36   6.261%   $109.8314   $109.83   $109.85   $109.80  
  Purchase #3 $177.91   8.707%   $193.4006   $193.40   $193.40   $193.40  
  Purchase #4 $162.67   9.333%   $177.852   $177.85   $177.85   $177.90  
  Purchase #5 $38.33   6.841%   $40.9522   $40.95   $40.95   $41.00  
  Purchase #6 $127.84   10.538%   $141.3118   $141.31   $141.30   $141.30  
  Purchase #7 $238.67   11.279%   $265.5896   $265.59   $265.60   $265.60  
  7 purchase totals = $967.57       $1,062.5371   $1,062.53   $1,062.55   $1,062.60