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 $194.94   8.521%   $211.5508   $211.55   $211.55   $211.60  
  Purchase #2 $96.79   12.263%   $108.6594   $108.66   $108.65   $108.70  
  Purchase #3 $22.87   13.864%   $26.0407   $26.04   $26.05   $26.00  
  Purchase #4 $165.54   10.532%   $182.9747   $182.97   $182.95   $183.00  
  Purchase #5 $217.84   5.747%   $230.3593   $230.36   $230.35   $230.40  
  Purchase #6 $23.35   6.384%   $24.8407   $24.84   $24.85   $24.80  
  Purchase #7 $145.95   13.707%   $165.9554   $165.96   $165.95   $166.00  
  7 purchase totals = $867.28       $950.3810   $950.38   $950.35   $950.50