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 $75.67   11.148%   $84.1057   $84.11   $84.10   $84.10  
  Purchase #2 $223.81   3.808%   $232.3327   $232.33   $232.35   $232.30  
  Purchase #3 $29.81   12.604%   $33.5673   $33.57   $33.55   $33.60  
  Purchase #4 $210.46   10.137%   $231.7943   $231.79   $231.80   $231.80  
  Purchase #5 $153.87   12.790%   $173.55   $173.55   $173.55   $173.60  
  Purchase #6 $108.88   5.648%   $115.0295   $115.03   $115.05   $115.00  
  Purchase #7 $149.85   7.232%   $160.6872   $160.69   $160.70   $160.70  
  7 purchase totals = $952.35       $1,031.0667   $1,031.07   $1,031.10   $1,031.10