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 $43.81   12.277%   $49.1886   $49.19   $49.20   $49.20  
  Purchase #2 $196.33   8.595%   $213.2046   $213.20   $213.20   $213.20  
  Purchase #3 $56.49   9.536%   $61.8769   $61.88   $61.90   $61.90  
  Purchase #4 $212.60   6.642%   $226.7209   $226.72   $226.70   $226.70  
  Purchase #5 $41.82   9.551%   $45.8142   $45.81   $45.80   $45.80  
  Purchase #6 $166.77   4.842%   $174.845   $174.85   $174.85   $174.80  
  Purchase #7 $148.33   11.816%   $165.8567   $165.86   $165.85   $165.90  
  7 purchase totals = $866.15       $937.5069   $937.51   $937.50   $937.50