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 $74.74   13.682%   $84.9659   $84.97   $84.95   $85.00  
  Purchase #2 $153.79   7.492%   $165.3119   $165.31   $165.30   $165.30  
  Purchase #3 $42.89   11.705%   $47.9103   $47.91   $47.90   $47.90  
  Purchase #4 $104.94   8.672%   $114.0404   $114.04   $114.05   $114.00  
  Purchase #5 $184.37   10.634%   $203.9759   $203.98   $204.00   $204.00  
  Purchase #6 $152.36   11.282%   $169.5493   $169.55   $169.55   $169.50  
  Purchase #7 $160.33   13.246%   $181.5673   $181.57   $181.55   $181.60  
  7 purchase totals = $873.42       $967.3210   $967.33   $967.30   $967.30