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 $76.68   3.717%   $79.5302   $79.53   $79.55   $79.50  
  Purchase #2 $126.98   5.251%   $133.6477   $133.65   $133.65   $133.60  
  Purchase #3 $197.95   10.395%   $218.5269   $218.53   $218.55   $218.50  
  Purchase #4 $247.31   10.356%   $272.9214   $272.92   $272.90   $272.90  
  Purchase #5 $54.80   7.331%   $58.8174   $58.82   $58.80   $58.80  
  Purchase #6 $155.85   8.438%   $169.0006   $169.00   $169.00   $169.00  
  Purchase #7 $39.90   5.649%   $42.154   $42.15   $42.15   $42.20  
  7 purchase totals = $899.47       $974.5982   $974.60   $974.60   $974.50