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 $45.64   6.499%   $48.6061   $48.61   $48.60   $48.60  
  Purchase #2 $194.92   12.338%   $218.9692   $218.97   $218.95   $219.00  
  Purchase #3 $102.55   4.848%   $107.5216   $107.52   $107.50   $107.50  
  Purchase #4 $197.48   11.663%   $220.5121   $220.51   $220.50   $220.50  
  Purchase #5 $182.33   7.258%   $195.5635   $195.56   $195.55   $195.60  
  Purchase #6 $246.58   10.164%   $271.6424   $271.64   $271.65   $271.60  
  Purchase #7 $91.67   3.175%   $94.5805   $94.58   $94.60   $94.60  
  7 purchase totals = $1,061.17       $1,157.3954   $1,157.39   $1,157.35   $1,157.40