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 $91.32   5.336%   $96.1928   $96.19   $96.20   $96.20  
  Purchase #2 $205.85   13.772%   $234.1997   $234.20   $234.20   $234.20  
  Purchase #3 $138.61   7.668%   $149.2386   $149.24   $149.25   $149.20  
  Purchase #4 $126.55   4.156%   $131.8094   $131.81   $131.80   $131.80  
  Purchase #5 $227.33   10.771%   $251.8157   $251.82   $251.80   $251.80  
  Purchase #6 $65.81   12.560%   $74.0757   $74.08   $74.10   $74.10  
  Purchase #7 $98.70   9.459%   $108.036   $108.04   $108.05   $108.00  
  7 purchase totals = $954.17       $1,045.3679   $1,045.38   $1,045.40   $1,045.30