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 $203.33   7.692%   $218.9701   $218.97   $218.95   $219.00  
  Purchase #2 $151.79   11.532%   $169.2944   $169.29   $169.30   $169.30  
  Purchase #3 $234.74   12.867%   $264.944   $264.94   $264.95   $264.90  
  Purchase #4 $48.65   10.272%   $53.6473   $53.65   $53.65   $53.60  
  Purchase #5 $45.49   13.621%   $51.6862   $51.69   $51.70   $51.70  
  Purchase #6 $214.33   4.177%   $223.2826   $223.28   $223.30   $223.30  
  Purchase #7 $146.74   12.513%   $165.1016   $165.10   $165.10   $165.10  
  7 purchase totals = $1,045.07       $1,146.9262   $1,146.92   $1,146.95   $1,146.90