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 $121.33   11.489%   $135.2696   $135.27   $135.25   $135.30  
  Purchase #2 $168.68   3.722%   $174.9583   $174.96   $174.95   $175.00  
  Purchase #3 $225.80   8.665%   $245.3656   $245.37   $245.35   $245.40  
  Purchase #4 $149.85   3.579%   $155.2131   $155.21   $155.20   $155.20  
  Purchase #5 $239.91   9.360%   $262.3656   $262.37   $262.35   $262.40  
  Purchase #6 $60.35   8.793%   $65.6566   $65.66   $65.65   $65.70  
  Purchase #7 $31.90   7.644%   $34.3384   $34.34   $34.35   $34.30  
  7 purchase totals = $997.82       $1,073.1672   $1,073.18   $1,073.10   $1,073.30